Wafer level chip scale package structure and manufacturing method thereof

ABSTRACT

A wafer level chip scale package (WLCSP) structure and a manufacturing method are disclosed. The WLCSP structure comprises a semiconductor die and a stack. The stack comprises a protective tape and a molding compound. A portion of a first interface surface between the molding compound and the protective tape is curved. The manufacturing method comprises the steps of forming a semiconductor structure; attaching the semiconductor structure on a dummy wafer; performing a first dicing process using a first cutting tool; depositing a molding compound; removing the dummy wafer; performing a second dicing process with a second cutting tool. A first aperture of the first cutting tool is larger than a second aperture of the second cutting tool. The portion of the first interface surface being curved reduces the possibility of generation of cracks in the WLCSP structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a Divisional Application of a pending application Ser. No. 15/197,609 filed on Jun. 29, 2016. The Disclosure made in the patent application Ser. No. 15/197,609 is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates generally to a semiconductor packaging technology. More particularly, the present invention relates to a wafer level chip scale package (WLCSP) structure and the method of manufacturing the WLCSP structures.

BACKGROUND OF THE INVENTION

Wafer level chip scale packaging (WLCSP) is a packaging technology of molding flip chips at a wafer level without using lead frames. WLCSP forms package structures having thinner body sizes. WLCSP is widely used in semiconductor packaging industry.

During packaging process and subsequent reliability test, cracks are frequently generated between layers of package structures. Minor cracks between a protective tape and a molding compound are often observed. Having the presence of minor cracks, it is more challenging to conduct subsequent backside treatment of semiconductor chips formed on the silicon wafer. Moisture, oxygen and other impurities may come into the package structures through the cracks; may erode components inside the package structures; and may affect the performance of the package structures.

SUMMARY OF THE INVENTION

A wafer level chip scale package (WLCSP) structure and a manufacturing method are disclosed. The WLCSP structure comprises a semiconductor die and a stack. The stack comprises a protective tape and a molding compound. A portion of a first interface surface between the molding compound and the protective tape is curved. The manufacturing method comprises the steps of forming a semiconductor structure; attaching the semiconductor structure on a dummy wafer; performing a first dicing process using a first cutting tool; depositing a molding compound; removing the dummy wafer; performing a second dicing process with a second cutting tool. A first aperture of the first cutting tool is larger than a second aperture of the second cutting tool. The portion of the first interface surface being curved reduces the possibility of generation of cracks in the WLCSP structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic diagram of a wafer level chip scale package (WLCSP) structure in examples of the present disclosure.

FIG. 2 is a top view of the WLCSP structure shown in FIG. 1.

FIG. 3-12 are cross-sectional schematic diagrams illustrating a method for manufacturing a wafer level chip scale package structure in examples of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross-sectional schematic diagram of a wafer level chip scale package (WLCSP) structure in examples of the present disclosure. The WLCSP structure includes a protective tape 11, a first metal layer (for example, a back metal) 12, a substrate (for example, a silicon substrate) 13, a second metal layer (for example, an aluminum layer) 14 and a passivation layer (PV) 15. The protective tape 11, the first metal layer 12, the substrate 13, the second metal layer 14 and the passivation layer 15 are arranged in the given order in a vertical direction. In examples of the present disclosure, the vertical direction is parallel to a thickness direction of the substrate 13. In examples of the present disclosure, the vertical direction is perpendicular to a bottom surface of the protective tape 11.

In examples of the present disclosure, the protective tape 11 has a raised center part and arc-shaped side edges. In examples of the present disclosure, an arc-shaped side edge is a curved interface surface (for example, a portion of an interface between the protective tape 11 and molding compound 17). In one example, an arc-shaped side edge has a constant radius of curvature. In another example, an arc-shaped side edge has a progressive changing of the radii of curvatures from a first end to a second end of the side edges. The first metal layer 12 is attached to a top surface of the raised center part of the protective tape 11. The silicon substrate 13 is attached to a top surface of the first metal layer 12. The second metal layer 14 is attached to a top surface of the substrate 13. The passivation layer 15 is attached to a top surface of the second metal layer 14.

In examples of the present disclosure, the WLCSP structure further comprises a plurality of connection members. Each connection member includes a metal pillar 16 (for example, a copper pillar) and a solder bump 18. Each connection member is electrically connected to the second metal layer 14 through an opening on the passivation layer 15. In one example, the metal pillar 16 goes through an opening formed on the passivation layer 15. A top surface of the metal pillar 16 is higher than a top surface of the passivation layer 15. A bottom surface of the metal pillar 16 is coplanar with a bottom surface of the passivation layer 15. In examples of the present disclosure, the second metal layer 14 has recesses to receive the metal pillars 16. The solder bump 18 is formed on the top surface of the metal pillar 16 for electrical connection with other components.

Molding compound 17 covers side walls of the metal pillar 16 and the top surface of the passivation layer 15. The molding compound 17 extends to cover side walls of the passivation layer 15, side walls of the second metal layer 14, side walls of the silicon substrate 13 and side walls of the first metal layer 12. The molding compound 17 covers the side edges of the protective tape 11. The arc-shaped surfaces at the side edges of the protective tape 11 increase the interface area between the molding compound 17 and the protective tape 11. Therefore, it strengthens mutual adhesion between the molding compound 17 and the protective tape 11. In examples of the present disclosure, without affecting the performance of the package structure, a respective interface surface between each of the first metal layer 12 and the molding compound 17, the substrate 13 and the molding compound 17, the second metal layer 14 and the molding compound 17, and the passivation layer 15 and the molding compound 17 has arc-shaped interface surface (similar to the arc-shaped surface between the molding compound 17 and the protective tape 11 as shown in FIG. 1). Therefore, it strengthens the mutual adhesion between the molding compound 17 and each of these layers. In examples of the present disclosure, the material for the first metal layer 12 is titanium (Ti), nickel (Ni) or silver (Ag).

FIG. 2 is a top view of the WLCSP structure shown in FIG. 1. In examples of the present disclosure, in FIGS. 1-2, a height A of the WLCSP structure ranges from 0.175 mm to 0.250 mm (preferably, 0.175 mm, 0.200 mm or 0.250 mm). A length D ranges from 0.585 mm to 0.615 mm (preferably, 0.585 mm, 0.600 mm or 0.615 mm). A width E ranges from 0.28500 to 0.315 mm (preferably, 0.285 mm, 0.300 mm or 0.315 mm). A length D1 of the connection member (including metal pillar 16 and solder bump 18) along the length direction D of the WLCSP structure (i.e., the lateral direction shown in FIG. 2) ranges from 0.090 mm to 0.190 mm (preferably, 0.090 mm, 0.140 mm or 0.190 mm). A width E1 of the connection member along the width direction E of the WLCSP structure ranges from 0.190 mm to 0.290 mm (preferably, 0.190 mm, 0.240 mm or 0.290 mm). A length D2 between adjacent connection members within the same WLCSP structure ranges from 0.210 mm to 0.310 mm (preferably, 0.210 mm, 0.260 mm or 0.310 mm).

The interface surface between the molding compound 17 and other layers is increased. It effectively increases the adhesion between the layers. The arc-shaped interface surfaces enhance the adhesion between the layers in the WLCSP structure. It effectively reduces the possibility of generating cracks between the layers in subsequent back treatment of the WLCSP structure, storage of the WLCSP structure and use of the WLCSP structure. It improves the performance of the package structure. The arc-shaped interface surface of two different materials suppresses the risk of product cracks, increase product yield, and improves quality and reliability. The arc-shaped interface surface arranged near the edge of the WLCSP structure improves the electrical conductivity and heat dissipation of the WLCSP structure.

FIGS. 3-12 are cross-sectional schematic diagrams showing a method for manufacturing the WLCSP structure of FIGS. 1-2. A plurality of WLCSP structures are fabricated from a wafer. For illustration purpose, FIGS. 3-12 only show fabrication of two WLCSP structures of the plurality of WLCSP structures. Each WLCSP structure has a plurality of metal pillars 24. For illustration purpose, FIGS. 3-12 show that each WLCSP structure has only two metal pillars 24 of the plurality of metal pillars 24.

The method may start from the step shown in FIG. 3. A second metal layer 22 (for example, an aluminum, Al) is deposited by sputtering (or other processes) on a top surface of a substrate 21 (for example, as silicon, Si). The top surface of the substrate 21 is an active area. A plurality of package units (two package units for illustration purpose, but not shown in FIG. 3) are associated with the top surface of the substrate 21. Each package unit is illustrated to associated with two metal pillars 24. A cutting space is arranged between two adjacent package units. The second metal layer 22 is used as a conducting layer for electric connection between the package units and the subsequently formed solder bumps 25 of FIG. 4. A passivation layer 23 is deposited on a top surface of the second metal layer 22. The passivation layer 23 is etched to form a plurality of openings. Portions of the top surface of the second metal layer 22 are exposed from the plurality of openings of the passivation layer 23. A plurality of metal pillars 24 (for example, copper pillars) are deposited on the exposed portions of the top surface of the second metal layer 22 The openings of the passivation layer 23 are entirely filled with the plurality of metal pillars 24. The plurality of metal pillars 24 connects to the top surface of the second metal layer 22. A top surface of the metal pillar 24 is higher than the top surface of the passivation layer 23.

As shown in FIG. 4, a respective solder bump 25 is deposited on the top surface of each metal pillar 24 so as to form a respective connection member. Two adjacent connection members within the same package unit are electrically connected via the second metal layer 22.

The substrate 21 is thinned from a backside. For example, a portion of the substrate 21 below the dotted line in FIG. 4 is removed so as to form a thinned substrate structure 21 shown in FIG. 5. As shown in FIG. 6, a first metal layer 26 (for example, a back metal) is formed, by sputtering or vapor deposition, on the back surface of the thinned substrate 21. In one example, the first metal layer 26 is a single-layer structure. In another example, the first metal layer 26 is a multi-layer structure. For example, the first metal layer 26 comprises materials selected from the group consisting of titanium (Ti), nickel (Ni) and silver (Ag). In examples of the present disclosure, the thickness of the first metal layer ranges from 8 μm to 10 μm.

As shown in FIG. 7, a protective tape 27 is attached to a back surface of the first metal layer 26. As shown in FIG. 8, the structure as shown in FIG. 7 is then attached to a dummy wafer 29 by a double side tape 28.

In FIG. 9, a pre-cut process is performed in the cutting space between two adjacent package units. The pre-cut depth is determined according to actual process requirements. In one example, the pre-cut does not cut through the protective tape 27 as shown in FIG. 9. In one example, the pre-cut cuts through the passivation layer 23, the second metal layer 22, the substrate 21, and the first metal layer 26. The pre-cut stops within the protective tape 27. A notch 30 formed by the pre-cut process has an arc-shaped bottom end. In one example, the arc-shaped bottom end has a constant radius of curvature (the area circled by the dotted line in FIG. 9) determined by a shape of the cutting tool.

As shown in FIG. 10, a molding compound 31 is filled in the notch 30 and in the space formed between the adjacent connection members. The molding compound 31 covers the side walls of the metal pillar 24 and the top surface of the passivation layer 23. The molding compound 31 extends to cover side walls of the passivation layer 23, side walls of the second metal layer 22, side walls of the substrate 21 and side walls of the first metal layer 26. The molding compound 31 covers the arc-shaped side edges of the protective tape 27 (the area at the bottom of the notch 30). In one example, the material of the protective tape 27 is different from the material of the molding compound 31. In another example, the material of the protective tape 27 is the same as the material of the molding compound 31

As shown in FIG. 11, the dummy wafer 29 and the double side tape 28 of the package structure of FIG. 10 are removed. A dicing process is applied by cutting along the direction indicated by an arrow 32 so as to form the individual WLCSP structures as shown in FIG. 12. The dicing process cut through the molding compound 31 filled over and in the notch and through the protective tape 27.

As shown in FIG. 11 and FIG. 12, the arc-shaped bottom end of the notch 30 results in the arc-shaped interface surface between the protective tape 27 and the molding compound 31. It effectively prevents the generation of cracks between the protective tape 27 and the molding compound 31 during the dicing process. In examples of the present disclosure, the pre-cut process and the dicing process are by laser cutting. The aperture of the cutting tool used in the dicing process is smaller than that used in the pre-cut process so that the final WLCSP structure comprises the arc-shaped interface surfaces. The arc-shaped interface surfaces increase the adhesion between the layers of the WLCSP structure, particularly between the protective tape 27 and the molding compound 31. It effectively reduces the possibility of generation of cracks between the layers of the WLCSP structure during back treatment, storage and use of the WLCSP structure. It improves the performance of WLCSP structure.

In addition to the arc-shaped interface surface between the protective tape 27 and the molding compound 31, the interface surfaces between the molding compound 31 and other layers (for example, the first metal layer 26, and the substrate 21) may be arc-shaped to increase inter-layer adhesion.

Those of ordinary skill in the art may recognize that modifications of the embodiments disclosed herein are possible. For example, the radius of curvature of the curved interface surface may vary. Other modifications may occur to those of ordinary skill in this art, and all such modifications are deemed to fall within the purview of the present invention, as defined by the claims. 

The invention claimed is:
 1. A method for manufacturing wafer level chip scale package (WLCSP) structures, the method comprising the steps of: forming a semiconductor structure comprising a plurality of semiconductor units; attaching the semiconductor structure on a dummy wafer; performing a first dicing process using a first cutting tool on the semiconductor structure to form a respective notch on the semiconductor structure between each set of two adjacent semiconductor units of the plurality of semiconductor units, a bottom end surface of the respective notch being curved; depositing a molding compound to cover a top surface of the semiconductor structure, the molding compound entirely fill the notches; removing the dummy wafer; performing a second dicing process with a second cutting tool on the semiconductor structure, the second dicing process cutting through the notches to form the WLCSP structures; wherein a first aperture of the first cutting tool is larger than a second aperture of the second cutting tool; wherein the step of forming the semiconductor structure with the plurality of semiconductor units comprises the sub-steps of: forming a chip array on a top surface of a substrate; and depositing a protective tape on a bottom surface of the substrate so as to form the semiconductor structure with the plurality of semiconductor units; wherein the sub-step of forming the chip array on the top surface of the substrate comprises the sub-steps of: providing the substrate, the substrate having a front side and a backside opposite the front side, the front side of the substrate comprising an active area; depositing a second metal layer, a passivation layer and a plurality of connection members on a top surface of the active area of the substrate, wherein the second metal layer covers the top surface of the active area of the substrate, the passivation layer covers a top surface of the second metal layer and the connection member is electrically connected to the second metal layer through openings formed on the passivation layer; thinning from the backside of the substrate; and depositing a first metal layer and the protective tape to cover a surface of a backside of the thinned substrate so as to form the chip array; and wherein each of the plurality of semiconductor units comprises at least one connection member of the plurality of connection members.
 2. The method for manufacturing the WLCSP structures of claim 1, wherein each connection member of the plurality of connection members comprises a metal pillar and a solder bump, and the sub-step of depositing the second metal layer, the passivation layer and the plurality of connection members on the top surface of the active area of the substrate comprises the sub-steps of: depositing the second metal layer on the top surface of the active area of the substrate and depositing the passivation layer to cover the top surface of the second metal layer; depositing a respective metal pillar through each opening formed on the passivation layer directly, the respective metal pillar being connected to the second metal layer; and depositing a respective solder bump on each metal pillar to form a respective connection member.
 3. The method for manufacturing the WLCSP structures of claim 1, wherein the semiconductor structure is attached to the dummy wafer by a double-side adhesive tape; wherein the first metal layer is sandwiched between the protective tape and the substrate; and wherein the double-side adhesive tape is sandwiched between the protective tape and the dummy wafer.
 4. A method for manufacturing wafer level chip scale package (WLCSP) structures, the method comprising the steps of: forming a semiconductor structure comprising a plurality of semiconductor units; attaching the semiconductor structure on a dummy wafer; performing a first dicing process using a first cutting tool on the semiconductor structure to form a respective notch on the semiconductor structure between each set of two adjacent semiconductor units of the plurality of semiconductor units, a bottom end surface of the respective notch being curved; depositing a molding compound to cover a top surface of the semiconductor structure, the molding compound entirely fill the notches; removing the dummy wafer; performing a second dicing process with a second cutting tool on the semiconductor structure, the second dicing process cutting through the notches to form the WLCSP structures; wherein a first aperture of the first cutting tool is larger than a second aperture of the second cutting tool; wherein forming a chip array on a top surface of a substrate comprises the sub-steps of: providing the substrate, the substrate having a front side and a backside opposite the front side, the front side of the substrate comprising an active area; depositing a second metal layer, a passivation layer and a plurality of connection members on a top surface of the active area of the substrate, wherein the second metal layer covers the top surface of the active area of the substrate, the passivation layer covers a top surface of the second metal layer and the connection member is electrically connected to the second metal layer through openings formed on the passivation layer; thinning from the backside of the substrate; and depositing a first metal layer and a protective tape to cover a surface of a backside of the thinned substrate so as to form the chip array; and wherein each of the plurality of semiconductor units comprises at least one connection member of the plurality of connection members. 